Catastrophic climate change is already starting to unravel life as we know it, said Bill McKibben, one of the nation’s leading and provocative environmental thinkers.

“We’re going to have to figure out how to stop focusing our economies on growth and start thinking about survival,” said McKibben, who helped raise awareness about global warming 21 years ago with his book “The End of Nature.”

He will speak tonight at Point Loma Nazarene University as part of the conference “Nurturing the Prophetic Imagination.” McKibben’s talk comes on the eve of the annual Earth Hour. Organizers ask residents, companies and agencies to turn off their lights for one hour tomorrow starting at 8:30 p.m. For more details, go to earthhour.org.

QUESTION: How much of a difference do campaigns such as Earth Hour, Earth Day and Step It Up make in bringing the world closer to sustainable levels of carbon dioxide, which trap heat in the planet’s atmosphere.

ANSWER: You can’t have political action on a tough topic unless there’s a movement there to build some real momentum. So that’s what we provide.

QUESTION: What is the focus of tonight’s talk? Will you discuss the international 350.org movement that you created?

ANSWER: I’ll try to bring people up to date on the state of climate science and urge them to join us in … 350.org. The number comes from what scientists say is the maximum safe level of carbon dioxide in the atmosphere. Our global day of action last fall involved 5,200 rallies in 181 countries.

QUESTION: What do you think are the most important ways people can contribute to a better environment in their everyday lives?

ANSWER: Organize politically in their communities and figure out how to link up with other communities to do the same on a larger basis. Look, we really can’t solve climate change one light bulb at a time. So do the obvious things at home, but save some of your creativity and passion for organizing on a larger scale.

QUESTION: What’s your take on the current state of environmental awareness and activism in the United States?

ANSWER: Somewhat behind the rest of the world because there’s been an organized disinformation campaign from our friends at the big energy companies. But more and more people are noticing the weird weather, and it’s clear from polls that a majority of Americans know global warming is real.

QUESTION: How optimistic are you about the world avoiding catastrophic climate change given the failure of the Copenhagen talks to produce an international accord last year? And what do you make of the increasing questions about some scientists’ research on global warming?

ANSWER: I’ve given up trying to figure out how optimistic or pessimistic I am. I get up every day and do what I can to build a movement big enough to make change, not knowing whether it will succeed in time. The science is undoubtedly dark, and that’s the reason scientists have come under fire. They’re bearing news that no one wants to hear.

After endless scrutiny, the deniers have shown a handful of mistakes (in climate documents). I think global warming researchers deserve our enormous thanks, not only for their work but for enduring really amazing abuse. From the earliest days at Scripps (Institution of Oceanography) in the 1950s, scientists have been heroes in this fight.

QUESTION: How will you celebrate Earth Day on April 22?

ANSWER: I fear I’ll be doing it the same way I did last year — giving speeches. Would that I were up in my north woods (in Vermont), you know, hugging some trees.